Method and an Apparatus for Access Network Selection in a Wireless Communication System

1. A method for selecting an access network by a user equipment (UE), the method comprising: determining whether at least one cellular access network of a first PLMN (public land mobile network) is overloaded; determining whether at least one wireless local area network (WLAN) access network is overloaded; and selecting one access network having a lowest load or congestion among the at least one WLAN access network based on information for an access network selection, when an ANDSF (Access Network Discovery and Selection Function) indicates that the UE unconditionally stays at a currently associated WLAN and the UE is connected to one of the at least one cellular access network, when all of the at least one cellular access network are determined to be overloaded or have been restricted for access to a predetermined time period, and when all of the at least one WLAN access network are determined to be overloaded or have been restricted for access to the predetermined time period, wherein the at least one cellular access network of the first PLMN is determined to be overloaded if a back-off timer for the predetermined time period is running for the at least one cellular access network, and wherein the predetermined time period is set by using history information, which is stored by the UE, and is related to at least one of an overload, congestion or load; selecting one access network among at least one cellular access network of a second PLMN when an ANDSF indicates that the UE conditionally stays at the currently associated WLAN, if all of the at least one WLAN access network are overloaded or have been restricted for access to the predetermined time period, wherein the second PLMN is one of an EPLMN (equivalent PLMN) or a PLMN which consists of only cellular access networks; and transmitting information using the selected one access network.

2. The method according to claim 1 , wherein the at least one WLAN access network is determined to be overloaded if a value of a load related parameter of the at least one WLAN access network is higher than a predetermined threshold.

3. The method according to claim 2 , wherein the load related parameter includes at least one of: information explicitly indicating that the at least one WLAN is overloaded, information on a total number of stations associated with at least one BSS of the at least one WLAN access network, information on a percentage of time that at least one access point (AP) of the at least one WLAN access network sensed that the medium was busy, information on a remaining amount of medium time available via an explicit admission control, information on a backhaul network to which the at least one WLAN is connected, or information on a throughput measured by the UE.

4. The method according to claim 1 , wherein information on the back-off timer is provided by a network node.

5. The method according to claim 1 , wherein the information for access network selection includes at least one of: information on a priority or preference for the at least one WLAN access network, load status or congestion information of at least one WLAN access network, load status or congestion information of at least one cellular access network, policy or rule information for an access network discovery and selection, subscription information, PDN connection information, information on whether to apply Multi Access PDN Connectivity (MAPCON), IP flow information, service information, bearer information, operator policy information, user preference information, local policy information, load status information of a core network, information on a roaming/non-roaming status of the UE, capability of the UE, time information, location information, history information on a load status of the at least one WLAN access network, or history information on load information of the at least one cellular access network.

6. A user equipment (UE) for selecting an access network, the UE comprising: a transceiving module; and a processor, wherein the processor is configured to: determine whether at least one cellular access network of a first PLMN (public land mobile network) is overloaded, determine whether at least one wireless local area network (WLAN) access network is overloaded, and select one access network having a lowest load or congestion among the at least one WLAN access network based on information for an access network selection, when an ANDSF (Access Network Discovery and Selection Function) indicates that the UE unconditionally stays at a currently associated WLAN and the UE is connected to one of the at least one cellular access network, when all of the at least one cellular access network are determined to be overloaded or have been restricted for access to a predetermined time period, and when all of the at least one WLAN access network are determined to be overloaded or have been restricted for access to the predetermined time period, wherein the at least one cellular access network of the first PLMN is determined to be overloaded if a back-off timer for the predetermined time period is running for the at least one cellular access network, and wherein the predetermined time period is set by using history information, which is stored by the UE, and is related to at least one of an overload, congestion or load, select one access network among at least one cellular access network of a second PLMN when an ANDSF indicates that the UE conditionally stays at the currently associated WLAN, if all of the at least one WLAN access network are overloaded or have been restricted for access to the predetermined time period, wherein the second PLMN is one of an EPLMN (equivalent PLMN) or a PLMN which consists of only cellular access networks, and transmit, via the transceiving module, information using the selected one access network.